It is often desirable to calculate the flow rate of a fluid traveling through a pipe. The method commonly used to determine the flow rate involves increasing the velocity of flow by causing the fluid to flow through a constriction. This results in an increase in the kinetic energy of flow accompanied by a corresponding drop in pressure at the constriction. The actual rate of flow can then be calculated by measuring the pressure before and after the constriction and applying the proper equations.
Of the devices used to determine flow rates, orifice meters have the simplest design, generally comprising an orifice plate which has a circular hole concentric with the pipe clamped between two pipe flanges. However, one circular hole may not be able to measure the flow rate in all cases. In order to get an accurate measurement in this instance, the flow of the fluid in the pipe must be stopped, the orifice plate removed and a new orifice plate having a circular hole of a different diameter inserted. Not only is this process cumbersome and time consuming, there is also considerable risk of injury to the operator who may inadvertently contact residual fluid in the pipes, which may be toxic, during the process of changing orifice plates. The present invention overcomes this deficiency by providing means for changing orifice plates without having to loosen or remove any part of the fitting.